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Wisconsin
Cranberry IPM
Newsletter volumed, lumbers, Ausustco, 1993
Integrated Pest Manatlpi|lfrlerlk fir Cranberries
CRANBERRY CARBON
BUDGET
About this time every year l get the
question ''What fertilizer can l add to make the
pinheads develop into large fruit's This question
makes the assumption that fertilizer is limiting to
fruit growth. lf you know that all of the major
elements are in the adequate range (see my article
in the last issue on tissue analysis) you know that
fertility is not the problem. If this is the case,
adding more fertilizer will not make pinheads set!
Two factors have been identified as
limiting to cranberry yields: the number of
fruiting uprights per ground area and to: number
of fruit per upright. Lets take these in reverse
order. The number of fruit per upright is
commonly known as fruit set. We could increase
yields markedly if we could set only one more
berg per fruiting upright. Several research
projects have shown that there is competition
between fruit on an upright for resources. That is
one reason why lower early forming fruit are
more likely to set than upper later forming fruit.
In my research program we have been
investigating how much carbohydrate is available
for vegetative growth or fruit growth. We
measured photosynthesis at intervals throughout
the season and occasionally throughout an entire
day. We then used this irtforluation to estimate
how much carbon an individual upright can ''fix''
during a season. This amount is roughly the
amount available for upright and fruit growth.
We then compared this to the amount of carbon
found in a typical fruit to see how many fruit
could be supported by an average upright. For
Stevens we found that a typical upright captures
about 0.45 grams of carbon during the course of
a year. Some of this carbon is used (be
respiration at night and some is used to create
new leaves and stems. We'Il estimate that is
about 20%. That leaves about 0.36 grams of
carbon available for fruit growth. A typical
Stevens berry weighs about 1.5 grams. About
85% of that weight is water leaving about 0.225
g dry weight. Roughly 5% of the dry weight is
the mineral fraction and the balance is lipid,
protein and carbohydrate. This comes to about
0.214 g. Not all of what remains is carbon (some
is hydrogen and orygen). Some researchers have
suggested multiplying this number by 0.45 to give
grams carbon. That gives 0.09 grams of carbon
per fruit. There is a respiratory cost associated
with growing the fruit that we estimate is equal to
the final carbon content giving a grand total of
0.18 grams of carbon per fruit.
Grams carbon fixed er u ri ht 0.45
Loss to res oration & rowth 0.09
Net carbon available er u Ii ht 0.36
Grams of carbon er mature fruit 0.09
Res irate cost of rowth 0.09
Total carbon cost er fruit 0. 18
When the arithmetic is all done we can
see that the amount of carbon available per
upright compared to the amount of carbon
required to grow a fruit allows for production of
about 2 fruit per upright. The point of this
exercise is to attempt to show that carbohydrates
are likely the limiting factors for fruit set. A
typical upright has enough carbon to support
roughly two fruit. You should also understand
that our estimates of photosynthesis are based on
all clear sunny days with adequate temperatures.
Our estimate of carbon available is likely too

The Cranberry Integrated Pest Management for Cranberries Newsletter, produced in collaboration with UW-Extension and UW-Madison researchers, provides current pest status and biology information, as well as methods of pest reduction, and pesticides.

Wisconsin
Cranberry IPM
Newsletter volumed, lumbers, Ausustco, 1993
Integrated Pest Manatlpi|lfrlerlk fir Cranberries
CRANBERRY CARBON
BUDGET
About this time every year l get the
question ''What fertilizer can l add to make the
pinheads develop into large fruit's This question
makes the assumption that fertilizer is limiting to
fruit growth. lf you know that all of the major
elements are in the adequate range (see my article
in the last issue on tissue analysis) you know that
fertility is not the problem. If this is the case,
adding more fertilizer will not make pinheads set!
Two factors have been identified as
limiting to cranberry yields: the number of
fruiting uprights per ground area and to: number
of fruit per upright. Lets take these in reverse
order. The number of fruit per upright is
commonly known as fruit set. We could increase
yields markedly if we could set only one more
berg per fruiting upright. Several research
projects have shown that there is competition
between fruit on an upright for resources. That is
one reason why lower early forming fruit are
more likely to set than upper later forming fruit.
In my research program we have been
investigating how much carbohydrate is available
for vegetative growth or fruit growth. We
measured photosynthesis at intervals throughout
the season and occasionally throughout an entire
day. We then used this irtforluation to estimate
how much carbon an individual upright can ''fix''
during a season. This amount is roughly the
amount available for upright and fruit growth.
We then compared this to the amount of carbon
found in a typical fruit to see how many fruit
could be supported by an average upright. For
Stevens we found that a typical upright captures
about 0.45 grams of carbon during the course of
a year. Some of this carbon is used (be
respiration at night and some is used to create
new leaves and stems. We'Il estimate that is
about 20%. That leaves about 0.36 grams of
carbon available for fruit growth. A typical
Stevens berry weighs about 1.5 grams. About
85% of that weight is water leaving about 0.225
g dry weight. Roughly 5% of the dry weight is
the mineral fraction and the balance is lipid,
protein and carbohydrate. This comes to about
0.214 g. Not all of what remains is carbon (some
is hydrogen and orygen). Some researchers have
suggested multiplying this number by 0.45 to give
grams carbon. That gives 0.09 grams of carbon
per fruit. There is a respiratory cost associated
with growing the fruit that we estimate is equal to
the final carbon content giving a grand total of
0.18 grams of carbon per fruit.
Grams carbon fixed er u ri ht 0.45
Loss to res oration & rowth 0.09
Net carbon available er u Ii ht 0.36
Grams of carbon er mature fruit 0.09
Res irate cost of rowth 0.09
Total carbon cost er fruit 0. 18
When the arithmetic is all done we can
see that the amount of carbon available per
upright compared to the amount of carbon
required to grow a fruit allows for production of
about 2 fruit per upright. The point of this
exercise is to attempt to show that carbohydrates
are likely the limiting factors for fruit set. A
typical upright has enough carbon to support
roughly two fruit. You should also understand
that our estimates of photosynthesis are based on
all clear sunny days with adequate temperatures.
Our estimate of carbon available is likely too